Rotary engines

The rotary engine was an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary in operation, with the entire crankcase and its attached cylinders rotating around it as a unit. Its main application was in aviation, although it also saw use before its primary aviation role, in a few early motorcycles and automobiles.

This type of engine was widely used as an alternative to conventional inline engines (straight or V) during World War I and the years immediately preceding that conflict. It has been described as "a very efficient solution to the problems of power output, weight, and reliability".

By the early 1920s, the inherent limitations of this type of engine had rendered it obsolete.

A rotary engine is essentially a standard Otto cycle engine, with cylinders arranged radially around a central crankshaft just like a conventional radial engine, but instead of having a fixed cylinder block with rotating crankshaft as with a radial engine, the crankshaft remains stationary and the entire cylinder block rotates around it. In the most common form, the crankshaft was fixed solidly to the airframe, and the propeller was simply bolted to the front of the crankcase.

This difference also has much impact on design (lubrication, ignition, fuel admission, cooling, etc.) and functioning (see below).

The Musee de l'Air in Paris has on display a special, "sectioned" working model of an engine with seven "radially disposed" cylinders. It alternates between "rotary" and "radial" modes to demonstrate the difference between the internal motions of the two types of engine.

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Wikipedia